Agroforestry systems improve phosphorus bioavailability and reshape soil fungal communities in acidic forest soils by mitigating aluminum-induced stress

Phosphorus limitation in acidic soils, compounded by aluminum (Al 3 + ) toxicity, poses significant challenges to forest productivity in South China. This study evaluated agroforestry systems combining Pinus massoniana with economically important plants: Alpinia oxyphylla (M1), Ficus simplicissima (M2), Amomum villosum (M3), and Curcuma longa (M4), compared to monoculture pine forests (CK). Agroforestry systems, especially M4, exhibited significant reductions in exchangeable Al 3+ and aluminum saturation in the rhizosphere, enhancing phosphorus availability and microbial biomass phosphorus (SMBP), with M4 recording an SMBP of 27.36 mg kg −1 and an SMBP/TP ratio of 8.93 %. Linear regression showed that exchangeable Al negatively correlated with available phosphorus and microbial biomass phosphorus, indicating that elevated Al 3+ levels suppress P availability and microbial P uptake. Litter carbon, cellulose, and lignin content did not differ significantly between monoculture and agroforestry systems, though agroforestry systems generally had higher litter carbon content. Fungal composition varied significantly, with Ascomycota, Basidiomycota, Mortierellomycota, and Chytridiomycota dominating. Agroforestry increased fungal diversity, particularly in M3. Clustering analysis revealed that litter carbon, Ascomycota, Mortierellomycota, pH, and acid phosphatase clustered together, while CEC, Chytridiomycota, Al 3+ , SMBP, and litter cellulose and lignin formed a separate group, suggesting links between soil properties and fungal groups. Fungal guilds showed significant shifts, with higher relative abundance of Unknown Saprotrophs and Wood Saprotrophs in M2 and M4, respectively. Network analysis revealed a moderately structured fungal community with low connectivity. Agroforestry systems incorporating Amomum villosum and Curcuma longa offer strategies to improve soil health, mitigate aluminum stress, and enhance phosphorus cycling in acidic soils. • Agroforestry systems improve soil chemical properites, and reduce Al³ ⁺ toxicity. • Agroforestry maximizes SMBP and facilitates phosphorus cycling. • Distinct shifts in fungal diversity between monoculture and agroforestry rhizospheres. • Fungal community shifts reflect reduced aluminum-phosphorus imbalances.